WMOD00288 ‎(2)‎

• Title: Twelve Basin Investigation - Volume I
• Prepared For: Bureau of Reclaimation
• Prepared By: Robert D. Elliot, Jack F. Hannaford, Russell W. Chaffer
• Date: 5/15/1973
• Weather Modification - Doc Type: Report

,

r

with nearby rawinsonde data to assess seeding potential. To answer these objections,
the Twelve Basin Investigation was initiated.
The objective of the investigation was to determine the potential increases in
precipitation and streamflow resulting from modification of cold orographic clouds

in the following twelve major river basins of the western United States:
l. Upper Colorado 7. Snake
2. Rio Grande 8. Upper Missouri
3. Truckee, Humboldt, and Walker 9. San Joaquin
4. Sacramento 10. Deschutes
5. North Platte 11. Bear-Wasatch
6. Gila 12. Yakima

Principal boundaries of these major basins and the stream gaging stations
selected for runoff analysis are shown on Figure 1.1-1. Potential increases were
determined as an average and on a seasonal basis for the period 1952-1971.
Section 1.2 describes the meteorological approach to'the investigation conducted
by North American Weather Consultants and Slcction 1.3 describes the hydrologic approach
to the investigation conducted by Sierra Hydrotech. The results of these investiga-
tions for the first seven major basins listed above are presented as Volume 1 of the
Twelve Basin Investigation. Volume 2 contains the results of the investigations
for th~ remaining five major basins.

1.2 Meteorological Approach
1.2.1 Selection of Cloud Seeding Model. An important aspect in the determin-
ation of cloud seeding potential was first delineated in detail in the evaluation of
the Colorado State University (CSU) Climax investigations. This aspect is the rela-
tion between seeding potential and cloud top temperatures which has been extensively
discussed in relation to the Climax investigations (Grant and Mielke, 1967; Grant
et a1., 1968; Mielke, et a1., 1970; Chappel, et al., 1971).
The approach in the Twelve Basin Investigation is the employment of a cloud
seeding model for the development of precipitation-temperature diagrams (P-T curves)
based upon historical precipitation and ra~'insonde data. From such sets of curves,
the see.ding potential could then be determined.
Two models were considered for the investigations, the CSU mean orographic
model (Grant, et al., 1969), and the area of effect model (Elliott, 1969). The CSU
model requires mainly cloud geometry and te:mperature inputs along with 24-hour pre-
cipitation data stratified by air mass temperatures. The model discriminates the
potential for seeding increases in the differences between calculated total condensate

1-2